Conventionally, an image forming apparatus which forms an image on a recording medium such as a sheet using decolorable coloring material, and a decoloring apparatus which decolors an image of decolorable coloring material that has previously been formed on a sheet for reusing the sheet are known.
Further, an image forming apparatus having the above-described decoloring apparatus in the apparatus is also known.
The decolorable coloring material is coloring material which can be decolored by a prescribed condition, such as to be heated at a prescribed decoloring temperature, for example.
When reusing a sheet, the above-described image forming apparatus superposes an image of decolorable coloring material, to form a new image.
That is, the above-described image forming apparatus, in a sheet in which an image of decolorable coloring material has been decolored by the above-described decoloring apparatus, superposes an image of decolorable coloring material on the decolored image of the decolorable coloring material, to form a new image.
In the above-described decolored image of the decolorable coloring material, the color thereof is merely decolored. Accordingly, the decolorable coloring material remains on the sheet, after the above-described decoloring.
For this reason, regarding the decolored image, a problem of security, for example, may occur sometimes. In addition, when a sheet is repeatedly reused, the visibility of an image which is to be newly formed on the sheet may deteriorate.
An image forming apparatus is known which, in order to solve the above-described security problem, and to improve the visibility of an image, once forms an image (a solid image, for example) for coating with decolorable coloring material, on the whole surface of the image of the decolorable coloring material to be decolored.
This image forming apparatus superposes an image of decolorable coloring material on the image for coating, to form a new image.
In addition, an image forming apparatus is also known, which forms an image using a ground tint printing art, as an object to solve the above-described security problem.
On the other hand, a hybrid type image forming apparatus is also known, which can form an image using the above-described decolorable coloring material and non-decolorable coloring material.
Further, an image forming apparatus is also known, which forms an image using a plurality of decolorable coloring materials having different decoloring temperatures.
However, even in these image forming apparatuses, the above-described security problem exists, and an image forming method and a decoloring method which are suited for solving this problem has been desired from users.
In addition, the above-described decoloring apparatus can decolor all images of decolorable coloring material formed on a sheet, but cannot selectively decolor images of a plurality of the above-described decolorable coloring materials having the different decoloring temperatures.